Microscopic heterogeneity and distribution characteristics of reservoirs controlled by a sequence framework: A case study of the Donghe sandstone reservoir in the Tarim Basin, SW China

Abstract

In this article, abundant coring analysis results from underground reservoirs were used to understand the characteristics of reservoir micro‐heterogeneity within a sequence stratigraphic framework, primarily including the distribution of reservoir particles, fillings, and pore‐throat heterogeneities. The vertical distribution pattern of the reservoir micro‐heterogeneity is then summarized, and the controlling effect of the sequence frameworks at different levels on the micro‐heterogeneity distribution is discussed. Generally, the micro‐heterogeneity within the quasi‐sequence decreases from bottom to top, which is characterized by coarsening grain size, increasing quartz content, decreasing feldspar, debris, clay mineral, and calcareous cement content. The pore volume and throat radius and pore–throat connectivity have also been better with weakening secondary pore development and permeability anisotropies. Differences are observed in the micro‐heterogeneity distribution between the retrograde quasi‐sequence group and the progradational quasi‐sequence group. The micro‐heterogeneity vertical distribution in the retrograde quasi‐sequence group shows one set of characteristics from bottom to top, in which the grain size becomes finer, the calcareous precipitation degree increases, and the micro‐heterogeneity of the reservoir generally shows enhanced trend upward; however, the micro‐heterogeneity vertical distribution in the progradational quasi‐sequence group shows the opposite characteristics. The micro‐heterogeneity of the reservoirs in the system tract also shows some regularity. The sea level in the high system tract has risen and fallen several times and shows a relative fallen trend overall, and the micro‐heterogeneity weakens while progressing upward. Reservoir micro‐heterogeneity variations in the sequence framework are of great significance for determining reservoir quality and performing predictions during oil and gas exploration and development.